Titanium alloy tubing is frequently used in hydraulic systems, such as on an aircraft, to hold fluid or carry fluid to various locations within the hydraulic system. The fluid in the tubing is often under high pressure. The tubing must be properly tested to 11/2 or 2 times the working pressure prior to use to insure that it will not rupture or fail during use. It is also important that the tubing not be damaged by the test equipment and that impurities not be permitted to enter the tubing during the test.
Autofrettage is frequently carried out on titanium tubing by subjecting the tubing to a high internal pressure that stresses the inner part into the plastic range and, when removed, leaves residual compression there and residual tension in the outer part. The autofrettage is carried out by placing fluid inside the tubing under very high pressure, not to exceed 85% yield. This pressure is often greater than the working pressure and is in the range of 11,000 to 16,000 psi for titanium alloy tubing.
All open ends of the tubing must be capped or plugged during the testing or autofrettage process. This is often difficult because the ends are frequently bare tubing without any fittings or threaded connections thereon. If the tubing to be tested is in place in an aircraft hydraulic system, the tubing must be restored to full working conditions after the test. The tubing is often connected by an industry standard cryofit that uses the bare, square, ends of the tubing to connect the tubing within the system. Present test fittings often damage or mar the inside or outside of the bare tubing making it unfit for further use. Removal of the damaged section by cutting the end off the tubing creates extra expense. Further, for hydraulic systems in place on aircraft, the end of the tubing may not be cut off. A fitting is needed that can be placed over the bare end of a tube to plug the end when fluid under high pressure is placed in the tubing.